1. Field of the Invention
This invention relates to an electroplating apparatus for supplying a plating solution to an upper surface of a substrate in order to plate the surface.
2. Discussion of Background
As is known, in the process of mastering a CD, data prepared by pre-mastering are recorded on a pre-mastered CD or the like. Based on this, first, a laser beam irradiates for exposure a photosensitive agent, which has been applied to the surface of a glass disc, for the purpose of making a glass master. In a developing process, a pit is formed on a resist surface, and then a metal master is made from this glass master by electroless plating. Subsequently, a metal mother is made from this metal master by electric plating, and finally a stamper is made from this metal mother by electric plating.
A conventional technique for performing the mastering process is known as a CD mastering apparatus comprising an electroplating apparatus including a cathode base having a recess on its upper end face and adapted to support a substrate, and a clamper disposed in the recess of the cathode base and adapted to clamp a peripheral edge portion of the substrate together with the cathode base through a contract ring. A plating solution is supplied onto the substrate so that plating is applied to the surface.
In the electroplating apparatus constituting the CD mastering apparatus, since a twist lock mechanism is disposed between the clamper and the cathode base so that the clamper and the cathode base are mechanically tightened to clamp the substrate which is to be subjected to plating, the clamping force is varied as the temperature is changed. As a result, a uniform clamping force is unobtainable. Further, since a frictional loss occurs when the substrate is tightened by the clamper, a strong clamping force is unobtainable.
Owing to such a variation of clamping force, etc., plating solution tends to enter a gap formed between the cathode base or contact ring and the substrate, and components of the plating solution are precipitated on the cathode base, etc. In an extreme case, not only the substrate but also the cathode base or contact ring are plated. If the growth of the deposit caused by the plating solution or the plating on the cathode base or contact ring is left as it is, a non-uniform current density results. This can be a cause for non-uniform thickness of the plating. Moreover, the overall resistance is increased due to a partially insufficient contact relation and the output voltage of a constant current power source connected to the electroplating apparatus increases. Because of this, a safety circuit is activated to stop the activation of the electroplating apparatus, thereby interrupting the operation in some instances. Furthermore, due to a local concentration of current, the substrate and the cathode substrate or contact ring sometimes suffer from a burn.
Accordingly, heretofore, it was necessary to wipe out the deposit caused by plating, or the plating grown on the cathode base or contact ring whenever the substrate is exchanged, in order to prevent a nonuniform deposition, interruption of an operation and a quenching loss of the substrate, etc. Consequently, the maintenance work is complicated at the time the substrate is exchanged.